ScalaTest User Guide

Getting started

Selecting testing styles

Defining base classes

Writing your first test

Using assertions

Tagging your tests

Running your tests

Sharing fixtures

Sharing tests

Using matchers

Testing with mock objects

Property-based testing

Asynchronous testing

Using Scala-js

Using Inside

Using OptionValues

Using EitherValues

Using PartialFunctionValues

Using PrivateMethodTester

Using WrapWith

Philosophy and design

Migrating to 3.0

Using OptionValues

ScalaTest's OptionValues trait provides an implicit conversion that adds a value method to Option, which will return the value of the option if it is defined, or throw TestFailedException if not.

This construct allows you to express in one statement that an option should be defined and that its value should meet some expectation. Here's an example:

opt.value should be > 9

Or, using an assertion instead of a matcher expression:

assert(opt.value > 9)

Were you to simply invoke get on the Option, if the option wasn't defined, it would throw a NoSuchElementException:

val opt: Option[Int] = None

opt.get should be > 9 // opt.get throws NoSuchElementException

The NoSuchElementException would cause the test to fail, but without providing a stack depth pointing to the failing line of test code. This stack depth, provided by TestFailedException (and a few other ScalaTest exceptions), makes it quicker for users to navigate to the cause of the failure. Without OptionValues, to get a stack depth exception you would need to make two statements, like this:

val opt: Option[Int] = None

opt should be ('defined) // throws TestFailedException opt.get should be > 9

The OptionValues trait allows you to state that more concisely:

val opt: Option[Int] = None

opt.value should be > 9 // opt.value throws TestFailedException

Next, we'll take a look at using EitherValues.

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